Patent GB-673370-A (GB)
Title: Improvements in or relating to hydraulic servo motors and the like
IPC: B64C13/24
Filed: 1949-06-02
Abstract: 673,370. Fluid-pressure servomotors ; liquid-pressure engines. HOBSON, Ltd., H. M., WESTBURY, R., and TYLER, S. R. May 12, 1950 [June 2, 1949], No. 14839/49. Classes 69 (ii) and 135. In a hydraulic servomotor arrangement of the kind in which a hydraulic actuator moves in a direction and to an extent determined by that of a control valve operated by a manually-operated input member, the input member is linked to a collapsable member which collapses under an excessive load applied by the input member when the control valve seizes and brings about the operation of a valve which shuts off the supply of hydraulic fluid to the control valve. Fig. 1 shows an actuator comprising a movable cylinder 13 connected to an aileron or other aircraft control surface 21 and a piston 11 connected to a fixed part 15 of the aircraft. The liquid in the cylinder is kept under pressure by a spring-loaded piston 16 adapted to force liquid through a hole 18 in the piston rod 12. The cylinder 13 is under the control of a valve 36 connected through a floating lever 32 to an input member 29 which is connected to the pilot's control column. The upper end of the lever 32 is pivoted at 33 to a collapsable member 23 as described in Specification 673,369 and comprising a tube 51 normally prevented from sliding in a housing 22 fixed to the cylinder 13, by balls 53 loaded by a spring-loaded conical ended plunger 52 and reset by a plug 58. Also fixed to the cylinder 13 are the control valve housing 25, which therefore follows-up the movement of the control valve, stops 24 engageable with a projection 30 on the input member 29, and further valve housings 26, 27, 28. The housing 26 contains non- return valves 151 which enable liquid to pass from one side of the piston 11 to the other as described in Specification 627,737 when a port 50 is open and the cylinder 13 is moved manually through the stops 24. The housing 27 contains an annular spring- loaded check valve 38 slidable on a plunger 60 and normally kept open by the motive liquid supply from the inlet 37. The lower end of the plunger 60 projects into an annular chamber 66 and controls a port 67 whereby the two ends of the cylinder 13 may be connected. The area of the port 67 is half the crosssectioned area of the plunger 60 which is therefore subject to equal upward loads by a given pressure in either end of the cylinder 13. The plunger 60 is normally maintained in the position shown by a pivoted member 62 bearing a leaf spring 61, a catch 64 on which engages a catch 65 on the tube 51. When the member 23 collapses, the catch 65 is released and the plunger 60 ascends under the pressure in one end of the cylinder 13. A collar 68 on the plunger then holds the valve 38 closed and the port 67 is open to connect the ends of the cylinder 13. The housing 28 is connected to the exhaust ports of the control valve 36 and to a main exhaust outlet 46 and contains a spring-loaded check valve 44 which is normally kept open by the motive liquid supply pressure acting on a piston 43. Thus if the motive liquid supply fails, the inlet and exhaust of the control valve are sealed, but the ends of the cylinder 13 are connected on movement of the control valve 36. In a modification, Fig. 2 (not shown) the complete arrangement shown in Fig. 1 is duplicated for two power cylinder working in tandem, the input member being connected to the floating levers 32 of each arrangement through a linkage including a lever having a projection adapted to engage stops such as 24. Fig. 3 shows an arrangement similar to Fig. 1 for two hydraulic cylinders 13, 13a working in parallel and coupled to the control surface through a differential link 73. Valves 160, 160a controlling the motive liquid supplyfrom independent sources are closed by their respective springs 78, 78a on release of the catches 77, 77a when the member 23 or 23a collapses. The motive liquid supplies through passages 82, 82a normally maintain spring-loaded ball clutches 79, 79a out of engagement with the respective piston rods 12,12a, but if one of the supplies fails the relevant cylinder 13 or 13a is locked in position and the pivot 75 or 75a of the differential link is fixed. The control valves 36, 36a are operated from an impact member 129 through a linkage including a yoke member 122 connected to the input member by a collapsable coupling 123 similar to those in the collapsable members 23. The coupling 123 is adapted to collapse to permit pivotal movement of the yoke member 122 if one of the control valves 36, 36a seizes. Fig. 5 shows an arrangement having two hydraulic motors 83, 83a each comprising a rotary shaft 88 carrying a pair of eccentrics 89, 90 and a swash plate 95. The eccentrics are actuated 'by six radially arranged pairs of pistons 91, 92, each pair being under the control of a spring-loaded distributer valve 93 actuated by the swash plate 95. The motors operate through gears 98, 98a, 99, 100 a threaded sleeve 101 engaging screw jacks 102 connected to parts of the control surface. The distributer valves 93 are connected through lines 96, 97 to the control valves 36, 36a which are connected to an input member 29 through a linkage 84, 86, 87, 87a, 187, 187a including a floating lever 84 one end 85 of which is pivoted to a screwed follow-up member 103 in the boss of the gear wheel 99. Valves 160, 160a adapted to cut off the motive liquid supply are operated through the collapsable members 23, 23a as described in connection with Fig. 3. The valves 160, 160a have, however, extensions 110, 110a adapted to connect the lines 96, 97 when the respective valve 160, or 160a is closed. Contacts 108, 109 are normally kept closed against a spring 107 by the motive liquid supply pressure on a plunger 106 but if either of the supplies fails the contacts 108, 109 or 108a, 109a are separated, causing a warning lamp to be illuminated. The tubular members 51, 51a of the collapsable members 23, 23a have grooved extensions 112, 112a between which are interlocking plungers 111, 111a as described in Specification 673,372 arranged when either of the members 23, 23a collapses to lock the other against collapse. If the hydraulic motors are connected to a common shaft through differential gearing each is provided with a pressure operated lock similar to that shown in Fig. 3 to lock the shaft of a motor the control valve of which has seized. If the hydraulic jacks shown in Fig. 3 are directly connected to the output member without any differential link 73, the fluid operated clutches 79, 79a are dispensed with and the opposite ends of a jack which fails are automatically connected by a bye-pass connection. The output member may alternatively vary the blade pitch or tilt the rotor head of a helicopter. Specification 673,371 also is referred to. Reference has been directed by the Comptroller to Specification 617,375.